This invention relates generally to cryoanalgesia and more particularly to devices and procedures for applying cryoanalgesia to the neuroaxis.
Management of acute and chronic pain has been a concern for as long as medicine has been practiced. Many methods of inducing analgesia and anesthesia have been developed. The use of chemical substances is perhaps the most common approach to pain relief. This approach requires suitable substances that are effective, safe to humans, and do not cause complications or abnormal reactions. Despite the great advances that have been made in the field of anesthesiology, and in the field of pain relief in general, there are still some drawbacks to chemical-based approaches. For instance, the anesthetics generally available today must be administered in carefully graduated doses to assure the patient""s well being, require extended periods of fasting prior to treatment, and are often accompanied by undesirable after effects such as nausea.
An alternate approach that avoids these drawbacks is cryoanalgesia, which is a safe and effective approach to providing prolonged pain relief without the complications or undesirable after effects often experienced with chemical-based approaches. As used herein, the term xe2x80x9ccryoanalgesiaxe2x80x9d refers to cooling or freezing of neuronal tissue (nerves, synapses, ganglia, etc.) to produce analgesia or anesthesia. Attempts to use tissue cooling or freezing to control pain have been known since antiquity. Surgery using cold packs and the painless amputation of frozen limbs during wartime are part of military medical history. In the nineteenth century, attempts were made to use tissue cooling to treat a wide range of maladies. Twentieth century studies have shown that the cooling or freezing of neuronal tissue reduces or eliminates pain by interrupting nerve conduction. Cooling neuronal tissue to temperatures in the range of zero to xe2x88x924 degrees centigrade, and sometimes below, causes analgesia lasting from days to weeks. Neuronal tissues cease functioning when sufficiently cooled, but before becoming frozen. Freezing neuronal tissue (i.e., reducing tissue temperature to xe2x88x924 to xe2x88x9220 degrees centigrade or below) causes profound long lasting, usually permanent but sometimes reversible, anesthesia of the innervated part. There may well be different outcomes of cooling and freezing, depending on whether the treatment is applied to neuronal axons or neuronal cell bodies (containing the nucleus).
A number of devices for the controlled cooling and/or freezing of small volumes of tissue are available. Rigid cryoprobes exist for percutaneous use or in open invasive surgical procedures. For example, cryoprobes are used for freezing a range of lesions from prostate tissue to metastatic cancers in liver. Neuronal tissue has been frozen with such devices for the relief of pain. Such devices have been in use for more than 20 years.
Cryocatheters or cryogenic catheters are of more recent evolution and have been used by way of the blood vascular route to destroy, by freezing, conducting tissues in the heart for the correction of cardiac arrhythmia. Such cyrocatheters are not designed for cryoanalgesia.
In both these types of systems, coolant gases under pressure are delivered to the tip of the instrument (i.e., the probe or catheter) where expansion of the gas is used to create temperatures as low as xe2x88x9260 degrees centigrade or below which cools or freezes the tissues in the local area around the tip. The size and configuration of the lesion created will depend in large part on a configuration of the tip. The effect obtained will depend upon the rate of cooling, degree of cooling, and the duration of cooling, as well as specifics of the tissue and environment.
While conventional cryoprobes used to treat neuronal tissue can produce excellent results, they generally can be used only for certain percutaneous procedures in which the target neuronal tissue is readily accessible by the rigid probes or for open surgical procedures. These restrictions greatly limit the opportunities for using cryoanalgesia. Accordingly, it would be desirable to have a device and method that would allow a more extensive use of cryoanalgesia.
The above-mentioned need is met by the present invention, which provides a catheter including a catheter body having a proximate end and a distal end, means for holding the distal end adjacent to a neuroaxis structure target, and means for internally delivering a coolant fluid to the distal end of the catheter body. In one possible embodiment, the catheter body is a tube having first and second chambers formed therein. The means for holding includes an expandable portion formed in the tube and a pressurized fluid source connected to the first chamber for inflating the expandable portion, and the means for internally delivering a coolant fluid includes a delivery tube disposed in the second chamber and a source of coolant fluid connected to the delivery tube. A temperature detector can be disposed on an external surface of the catheter body.
The present invention can also include an electrically conductive tip member formed on an external surface of the catheter body, an external electrode for application to a patient""s body, and a monitoring/stimulating device electrically connected to the tip member and to the external electrode. The device is capable of delivering an electrical stimulus to the external electrode and measuring sensory evoked potentials in response to input from the tip member.
In use, the distal end of the catheter is inserted into the subarachnoid space of a patient and positioned adjacent to a neuronal tissue target. A portion of the catheter is inflated to hold the distal end in position on the target neuronal tissue. The external electrode is placed on a dermatome on the patient that corresponds to the neuronal tissue target. The monitoring/stimulating device can then be used to deliver an electrical stimulus to the dermatome (which will be transmitted centrally over sensory afferent nerve fibers) and measure resultant sensory evoked potentials detected at the tip member. Measurement of sensory evoked potentials can be used to verify that the distal end is properly positioned relative to the neuronal tissue target, since coolant fluid is delivered into the catheter so as to effect cooling or freezing of the neuronal tissue target and stop neuronal nerve conduction.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.